Hitherto, there has been known a so-called mechanical power-splitting (split type or two-motor type) hybrid driving unit, to be mounted in a vehicle, in which an engine, a generator and a driving (assist) electric motor are connected, respectively, to three elements of a planetary gear. The driving electric motor is coupled with an output shaft, output torque of the above-mentioned planetary gear is continuously controlled through control of the generator, and torque of the other driving electric motor is combined with the output torque of the planetary gear to be outputted to the output shaft as necessary.
A hybrid driving unit like that described above is disclosed, for instance, in Japanese Patent Laid-Open No. Hei. 08-183347 as a unit for a front-engine and front-drive (hereinafter “FF”) type vehicle and in Japanese Patent Laid-Open No. 2002-225578 as a unit provided with a transmission between an electric motor and an output shaft.
The position and direction of the hybrid driving unit to be mounted and the shape of a casing member vary from those of the FF type vehicle in mounting such unit to a front-engine and rear-drive (hereinafter “FR”) vehicle.
For instance, in the FR-type vehicle, an internal combustion engine, the hybrid driving unit and a propeller shaft are disposed approximately on one and the same axial line, in order, from the front side of the vehicle in the longitudinal direction of the vehicle's body. The hybrid driving unit is stored in a cylindrical casing member such that two electric motors (power generating first electric motor and a driving second electric motor), a power-splitting mechanism, a transmission and others are disposed at different positions on one and the same axial line.
From the aspect of mountability to the body, it is preferable to form the hybrid driving unit such that the front end thereof, which is coupled with the internal combustion engine, is thick and the rear end thereof, which is on the side of the propeller shaft, is thin. Further, with regard to the two electric motors described above, the radial dimension of the driving electric motor is apt to be larger than that of the power generating electric motor because the driving electric motor must generate a large torque in starting the vehicle. It is noted that if the radial dimension of the driving electric motor is suppressed, the length thereof in the longitudinal direction needs to be extended in order to assure high torque required in starting the vehicle. Accordingly, the length of the whole hybrid driving unit in the longitudinal direction also needs to be extended, thus degrading the mountability to the body.